Solar energy receiver

ABSTRACT

A solar energy receiver comprises a panel, having a graphite core, a substantially gas tight housing encasing the graphite core, a heat exchanger comprising heat exchanger tubing, a heat exchanger inlet and a heat exchanger outlet. The heat exchanger tubing is at least partially embedded in the graphite core, and the heat exchanger inlet and the heat exchanger outlet extend through the housing. The housing is sealed around the heat exchanger inlet and the heat exchanger outlet. A method of manufacturing a solar energy receiver comprises: a) fabricating the heat exchanger in a serpentine coil shape; b) inserting grooved planks of graphite between individual coils of the heat exchanger to form the graphite core such that the coils are encompassed in the grooves; c) inserting the graphite and heat exchanger into the housing; and d) sealing the housing and sealing openings around the inlet and outlet where they pass through the housing.

TECHNICAL FIELD

The present invention relates to the fields of solar energy conversionand in particular to devices for collecting solar energy as heat andstoring heat whereby its use is not directly linked to the availabilityof sunlight.

BACKGROUND OF THE INVENTION

Worldwide there is an increasing awareness of the need to reducereliance on fossil fuels and increase the use of renewable energysources. One major renewable energy source that is effectively unlimitedin the foreseeable future is solar energy, however solar energy has thedisadvantage that it is not available at night and during cloudy periodsand so conversion systems need to include some form of energy storage ifthey are to become a viable replacement for fossil fuel as a source ofenergy.

Existing solar energy conversion systems fall into several categories:—

1) Photovoltaic (PV) systems, in which solar energy is absorbed intomaterials that convert the solar energy directly into electricity;2) Concentrating Solar Power (CSP), in which solar energy is used toheat a fluid and that heated fluid is used to directly or indirectlydrive a mechanical device (such as a turbine) to convert the heat energyinto electrical energy.

To enable solar radiation to be used as heat for a thermodynamic cycleto produce process steam or electricity, it must be first concentratedto achieve higher temperatures, as solar radiation reaches the earth ata density too low to directly produce such temperatures. A variety oftechnologies are being developed for use in CSP Systems including:—

Trough and “Fresnel” type linear collector systems, which comprise anelongate reflector, and one collector tube or assembly of tubes runningalong the focal point of the reflector. The tube(s) contains a fluidwhich is heated and then pumped to a heat engine (e.g. a turbine);

Tower systems which collect solar energy concentrated to a target from alarge number of mirrors which track the sun and focus the large numberof images at one collection point (heliostats), where the hightemperatures achieved are used to heat a fluid which is transmitted to aheat engine (e.g. a turbine). Tower systems may include single towersand multiple tower arrangements;

Dish/Engine systems, where a small heat engine is placed at the focalpoint of a parabolic dish and driven directly by the concentrated solarenergy.

Within the category of tower systems one arrangement that has shownpromise is the use of a graphite body as a solar receiver in which heatexchanger tubes are embedded where the heat exchange fluid used to drivean engine such as a turbine is directly heated by heat energy stored inthe graphite body. Such systems are in their infancy and existingconfigurations have a variety of disadvantages typical of early stagetechnologies including high cost of manufacture and structural integrityproblems. In particular, present designs (or at least those which havebeen shown to be practical) comprise a gas tight containment housingwhich encompasses most of the remainder of the assembly and this designplaces constraints on the manufacture of the receiver such as:—

-   -   If receivers are to be of a size that achieves reasonable        efficiency and cost effectiveness, they must be fully assembled        and tested at or near site, typically from outsourced        sub-assemblies. Due to the gas tight nature of the housing this        assembly operation is not trivial and adds considerably to the        expense of manufacture;    -   If assembly were to be contemplated at a site remote from the        installation site, overall dimensions of receivers are        constrained by road transport limitations and even with onsite        assembly there is a limitation on the size of subassemblies that        can be readily transported;    -   Graphite and heat exchanger piping costs amount to only 45% of        total cost of the receiver. Other major costs relate to the        containment housing and other structural items 16%, insulation        10% (of which 7% is for the shield protecting the base        structure);    -   The design requires many sub-assemblies and the resultant supply        chain has many vendors;    -   The need to ship unassembled parts and to assemble the parts on        site makes it expensive. Alternatively, shipping assembled units        would be difficult, if not impossible and prohibitive in cost;    -   The present receiver designs have limited scalability options        without total redesign and so the external dimensions, graphite        mass and potential power handling capacity are effectively        fixed;    -   Preparation of the receiver at site before installation on the        tower is time consuming;    -   Dimensional constraints imposed on the receiver design by        transport limitations restrict utilization of graphite in        previous designs to at best 70% to 75% because the constraints        on the design do not allow maximized usage of the standard        manufactured sizes of graphite block.

Throughout this specification, unless otherwise specified, panels ofsolar receivers will be described in a vertical orientation withvertical side walls at least one of which is a solar energy receivingwall. The panels and their components will be described as having a topand a bottom and two ends relative to the vertical side walls, and willinclude a top and bottom walls, and end walls, however the panels may beused in other orientations in which, for example a horizontalorientation in which the side wall may be at the top and a top wall maybe at the side.

SUMMARY

According to one aspect, the present invention consists in a solarenergy receiver comprising a panel, the panel comprising a graphitecore, a substantially gas tight housing encasing the graphite core, aheat exchanger comprising heat exchanger tubing including a heatexchanger inlet and a heat exchanger outlet, the heat exchanger tubingat least partially embedded in the graphite core, the heat exchangerinlet and the heat exchanger outlet extending through the housing andthe housing sealed around the heat exchanger inlet and the heatexchanger outlet.

According to a second aspect, the present invention consists in methodof manufacturing a solar energy receiver comprising a panel, the panelcomprising a graphite core, a substantially gas tight housing encasingthe graphite core, a heat exchanger comprising heat exchanger tubingincluding a heat exchanger inlet and a heat exchanger outlet the heatexchanger tubing at least partially embedded in the graphite core, theheat exchanger inlet and the heat exchanger outlet extending through thehousing and the housing sealed around the heat exchanger inlet and theheat exchanger outlet, the method comprising:

-   -   a) fabricating the heat exchanger in a serpentine coil shape;    -   b) inserting grooved planks of graphite between individual coils        of the heat exchanger to form the graphite core such that the        coils are encompassed in the grooves;    -   c) inserting the graphite and heat exchanger into the housing;        and    -   d) sealing the housing.        The heat exchanger may further comprise a heat exchanger drain        which also extends through the housing and the housing is sealed        around the heat exchanger drain.

The heat exchanger drain may also act as an inlet/outlet such that onlyone other inlet/outlet is required to pass through the housing wall. Theworking fluid may pass between the inlet/outlets in either directiondepending on the location of the panel in the solar receiverinstallation:

The drain may be configured to also be used as the inlet to the heatexchanger and the outlet will be located at the top of the receiverpanel such that flow of working fluid through the panel is from bottomto top through the panel.

The housing may have two spaced apart side walls joined together abouttheir periphery by one or more additional walls to form a closedcontainer. One of, or a portion of the one or more additional walls is abottom wall forming a base of the housing and in one embodiment thegraphite core will be located in thermal communication with the base andat least one of the two side walls of the housing. At least 2 walls ofthe housing may be in thermal communication with the graphite core. Thebottom wall of the housing may also be formed by bending a single pieceof wall material into a “U” shape having curved bends in which thebottom wall transitions into each of the side walls to which it isconnected via one of the curved bends. The curved bends at the edges ofthe bottom wall will reduce stresses in the housing wall allowing theuse of lighter wall construction and eliminating the need for furtherstructural support in the base wall. The walls of the housing may befabricated from 253MA austenitic stainless steel or any other hightemperature thermally conductive material (e.g. 800H or Inconel alloys)finished to mill finish class 2B. Depending upon the location of thesurfaces within the final receiver configuration and the geographiclocation of the installation, some surfaces may be provided with aspecific thermal emittance while others may be provided with a specificthermal absorptance to enhance performance. Surface treatments orsurface coatings may be applied to achieve specific emissivity in therange of 0.2-1.0. For example, if some surfaces are required to beemittive they may be left natural (specific emissivity 0.7) may bepolished (specific emissivity 0.2-0.3), or may be coated with or surfacetreated to achieve a specific emissivity in the range of 0.3-0.8 whileother surfaces which are required to be highly thermally absorptive maybe coated with or surface treated to achieve a highly heat absorbingsurface (such as a black surface with a specific absorptivity of0.8-1.0, preferably 0.9-1.0).

The other walls of the housing may also comprise a top wall opposite thebottom wall, and two end walls. The housing may also include a pluralityof mounting flanges extending from the housing and capable of suspendingand supporting the weight of the receiver element. The mounting flangesmay extend from joins between adjoining walls of housing and may includeholes for attachment to a mounting frame. For example the flanges mayextend from joins between the side walls and the end walls of thehousing. Each mounting flange may comprise an extension of one of theend walls beyond the respective side wall to which it is joined.Alternatively each mounting flange may comprise an extension of one ofthe end walls beyond the top wall. The mounting flanges may extend froman end wall that in use is typically oriented vertically. By suspendingthe receiver element rather than supporting it from below, the resultingtension in the side walls due to gravity of the graphite core acting onthe housing allows them to resist buckling to maintain good thermalcommunication with the graphite core. The shape of the housing alsotends to keep the metal walls pressed against the graphite core. Inaddition, by suspending the receiver from above, the base of the housingis exposed to, and can absorb, solar irradiation which would otherwisebe reflected by shielding tiles used in prior art designs to protect thebase structure from overheating.

The graphite core may be shaped to conform to the internal shape of thehousing and in particular has a portion shaped to conform to the shapeof the curved bends of the bottom wall of the housing. The graphite coremay comprise a plurality of stacked graphite planks, at least a lowerone of which is profiled to match the shape of the curved transitionsbetween the base and the lower portions of the side walls.

Graphite cores in prior art receivers were surrounded by insulation(except for the energy receiving surfaces) and the core and insulationwere housed in an inert gas environment to prevent chemical reaction ofthe core. The inert gas was generally maintained at a positive pressureto prevent leakage of air into the complex housing structure. Incontrast, embodiments of the present receiver have a simplified housingwhich has greater structural integrity. There is also no internalinsulation within the housing and the graphite core conforms to theinner shape of the housing. Therefore the amount of space left in thehousing is quite small after the graphite and heat exchanger areinserted and the housing is sealed, and it is possible to leave thisremaining space filled with air. On the first heating of the receiverelement a small amount of graphite will oxidize until the oxygen in theair is consumed, leaving the spaces substantially filled with nitrogenand carbon dioxide protecting the graphite from further oxidation whenexposed to high temperatures in subsequent thermal cycles. However ifthe operating temperature of the panel is to exceed 700° C. a reductionreaction may occur causing the carbon dioxide to reduce to carbonmonoxide with further carbon being consumed by the liberated oxygen.Subsequent cooling can lead to some of the carbon monoxide decomposingto carbon and oxygen which again forms carbon dioxide. This can lead todeterioration of the physical structure of the graphite over time.Therefore if the operating temperature of the panels is expected toexceed 700° C. in a particular installation, it will be desirable atmanufacture to replace the air filling the spaces in the panel betweenthe graphite and the walls with an inert gas such as argon or helium.Alternatively the spaces in the panel may be filled with thermallyconductive material that exists in a solid, liquid or gaseous state atleast in the working temperature range of the panel, such as tin, zinc,mercury, or a molten salt such as potassium nitrate, potassium nitrite,sodium nitrate, sodium nitrite, other nitrate, nitrite, chloride orfluoride salts or a mixture of such salts or graphite powder. Areservoir containing graphite powder may be located in communicationwith the interior of the housing, whereby graphite powder is suppliedfrom the reservoir to the interior of the housing to fill additionalvoid space created by expansion of the housing.

The points where the heat exchanger inlet and heat exchange outlet passthrough the housing may be in close proximity and may be at one end ofthe top wall of the housing, to assist with mounting and manifolding thepipes with other receivers. Alternatively, the drain, which is locatedat the lowest point of the heat exchanger, may double as one of theinlet/outlets, in which case only one inlet/outlet is required to beprovided at the top of the heat exchanger.

At least some of the heat exchanger tubes may be fabricated in a coiledor serpentine form suitable for compression (like a spring) duringassembly, such that when the container expands due to thermal expansion,the resulting stresses from the movement of the pipe configuration donot exceed the mechanical properties of the pipe material.

The heat exchanger coils may comprise a plurality of straight tubeportions arranged to be parallel to each other and connected at theirends to form one or more serpentine or coil shapes. In some embodimentsthe straight tube portions are arranged in parallel planes forming rowsof straight tube portions. The straight tube portions may be arranged incoils where rows of straight tube portions are interconnected at theirends and each row is connected to the row above and below to form asingle coil structure. Alternatively the straight tube portions may eachbe connected at respective ends to a straight tube portion above andbelow to form parallel serpentine constructions. Where the straight tubeportions form parts of coils there may be an even number of straighttube portions (such as two straight tube portions) in each row. Thestraight tube portions in each row may be aligned with the straight tubeportions in adjacent rows such that they also form planes perpendicularto the first mentioned parallel planes. At a first end of the heatexchanger (which will become the insertion end for subsequent insertionof graphite planks) the straight tube portions in each row may beconnected in pairs by first U-shaped connecting tube portions. At asecond end of the heat exchanger (the non-insertion end), the straighttube portions in each row may be connected to straight tube portions ineach of the two adjacent rows by second U-shaped connecting tubeportions. In the case where there are two straight tube portions perrow, the two straight tube portions in each row may therefore beconnected together at the first (insertion) end and each of the twostraight tube portions in each row are respectively connected tostraight tube portions of each of two adjacent rows at their second(non-insertion) end. A heat exchanger inlet tube and a heat exchangeroutlet tube may be connected to one of the straight tubes in each of toprow of straight tube portions and bottom row of straight tube portionsvia interconnecting tube portions.

Where the straight tube portions form serpentine constructions, theremay be an even number or an odd number of straight tube portions (suchas two or three straight tube portions) in each row. The straight tubeportions in each row may be aligned with the straight tube portions inadjacent rows such that they also form planes perpendicular to the firstmentioned parallel planes. At a first end of the heat exchanger each ofthe straight tube portions in each row may be connected by firstU-shaped connecting tube portions to straight tube portions in the rowbelow. At a second end of the heat exchanger, each of the straight tubeportions in each row may be connected to straight tube portions in rowabove by second U-shaped connecting tube portions. In this arrangementthe graphite planks are inserted from alternate ends of the serpentinestructure such that the planks are always inserted between two rows ofstraight tube portions at an end opposite the end at which those tworows are interconnected.

The configuration of the heat exchanger tubing and drain may be arrangedto allow drainage of liquid from top to bottom of the heat exchangerboth when the heat exchanger is in a vertical orientation (i.e. wherethe are coils stacked vertically above one another) and when the heatexchanger is angled from the vertical orientation (with the mountingpoints on the upper side) as when the panels are configured in aninverted “V” configuration. In one embodiment where the straight tubeportions form a coil structure, the heat exchange may be angled at anangle of up to 21°, however this angle is dictated by the angle of thesecond “U” shaped connecting tube portions which interconnect straighttube portions of different rows of straight tube portions and may bevaried depending on the angle of interconnection of adjacent rows ofstraight tube portions. The angle by which the heat exchanger deviatesfrom the vertical orientation should not exceed the angle of the second“U” shaped connecting tube portions (with respect to the plane of a rowof straight tube portions), such that condensed liquid in the heatexchanger is not required to flow up hill to reach the drain. In theserpentine structure the heat exchanger may be readily angled at anglesof up to 45° and possibly even approaching 90° to the vertical.

After the heat exchanger, is fabricated, pre-shaped planks of graphiteare positioned to be located between each row of tubes and cappingplanks are placed over the inlet end rows of straight tube portions andthe outlet end row of straight tube portions. The abutting surfaces ofthe graphite planks may have a surface finish which is N8 or better (ISO1302). The graphite planks (excluding the capping planks) each includetwo grooved surfaces, on opposite surfaces thereof, where the groovesmay be semi-circular in cross-section conforming to the shape and radiusof the straight tube portions and interconnecting tube portions at thefirst (insertion) end of the heat exchanger when the tube portions andthe surrounding graphite are at their working temperature such that whenassembled between rows of straight tube portions adjacent pairs of theplanks encompass and closely conform to the respective straight tubeportions and first connecting tube portions. To achieve close conformityof the heat exchanger tubes with the grooves in the graphite at theinternal working temperature of the panel, which is up to 800° C., thegrooves are made approximately 1.6% bigger than the nominal outsidediameter of the tubes to allow for the radial expansion of the tube atworking temperature with a tolerance of approximately +0.00/−1.00%. Forexample, when the heat exchanger tubes (made for example from 253MAaustenitic stainless steel, or any other suitable high temperaturethermally conductive material like 800H austenitic steel or alloys suchas Inconel) have a nominal outside diameter of 26.67 mm the grooves willbe 27.1 mm (+0.00/−0.25 mm) in diameter. Alternatively when the heatexchanger tubes made from the same or a similar material have a nominaloutside diameter of 42.16 mm the grooves will be 42.9 mm (+0.00/−0.25mm) in diameter. The smoothness of the surface of the grooves will havea bearing on heat transfer with smooth surfaced grooves having a highercontact surface than rough surface grooves, however the smoother thesurface the more expensive the cost of finishing the grooves.

The surface within the grooves may have a surface finish which is N7 orbetter (ISO 1302). Rather than being semicircular, the grooves may alsobe a half obround shape with a radius which is slightly greater (byabout 1.6% with a straight section about 1.6% of the radius in thedirection perpendicular to (i.e. across) the parallel groove, toaccommodate lateral movement of the tube when the coils expand. Howeverthis has the disadvantage that the tubes will not be as closelyencompassed in the grooves and in some cases it may be preferable toaccommodate expansion of the coils by other means such as by allowingthem to expand into the cavity which accommodates the second connectingportions.

At the second (non-insertion) end of the heat exchanger, ends of thegraphite planks are recessed to accommodate the second connecting tubeportions joining straight tube portions from adjacent rows of straighttube portions.

Capping planks are provided at either end of the stack of graphiteplanks. A lower capping plank is grooved on one surface facing anadjacent graphite plank the grooves conforming to the shape and radiusof the straight tube portions and interconnecting tube portions at thefirst (insertion) end of the heat exchanger. Edges of the lower cappingplank between the face opposite the adjacent graphite plank and thesides of the lower capping plank are radiused. An upper capping plank ispreferably recessed on a surface facing an adjacent graphite plank toaccommodate inlet and outlet tubing without constraining thermalexpansion thereof. As an inlet and outlet of the heat exchanger arefixed to the top wall of the housing where they pass through thehousing, the recess in the upper capping plank accommodates longitudinalexpansion of the tubes as well as allowing the coils, to separate orcompress with differential movement between the graphite and the housingas the housing expands and contracts with heating and cooling betweenambient and its upper working temperature, which can be as high as 1000°C. In the present embodiment the volume of void spaces within thehousing not occupied by graphite or tubing is generally in the range of4-10% and typically 5-7% of the internal volume of the housing (at theworking temperature). Correspondingly the side panel of the housing,which is the irradiated surface of the panel when in use, is generallybacked by the graphite core over all but 1-5% of its area and typically2-3% (at the working temperature) in the preferred embodiment.

The first (insertion) ends of the straight tube portions may be sprungapart slightly to allow the planks to be easily inserted into thefabricated heat exchanger tubing past the first connecting tube portionsand between adjacent rows of coils. Alternatively during fabrication ofthe heat exchanger coils, they may be spaced by a spacing greater thanor equal to a plank thickness of the graphite planks between which theyare located in the final assembly (or at least the first (non-insertion)ends may be so spaced), such that the planks may be easily inserted intothe fabricated heat exchanger tubing between adjacent rows of coils andthe coils of the tubing may then be compressed into contact with thegraphite after insertion of the graphite planks between the coils.

A solar energy receiver may comprise two or more receiver panelsconfigured and mounted to form a downward opening cavity. The cavity maybe formed with a combination of receiver panels and insulation panels.Outside surfaces of the receiver panels forming the solar energyreceiver may also be covered by insulation.

The solar energy receiver may comprise a plurality of receiver panelsarranged to form an opening, which is in a shape of a rectangular prism.The top of the rectangular prism opening may be closed by one or moreadditional receiver panels or may be closed by insulation on transparentpanels such as fused quartz. An underside of the insulation closing thetop of the rectangular prism shaped opening may have a high emissivitysurface facing into the opening.

Alternatively the solar energy receiver may comprise a plurality ofreceiver panels arranged in an inverted “V” configuration to form anopening which is in a shape of a triangular prism (with the lowerparallelogram side horizontal). The ends of the triangular prism shapedopening may be closed by further receiver panels or may be closed byinsulation panels or panels of optically transparent material such asfused quartz which can pass solar energy directed from the heliostats tothe skies of the receiver while confining convection within the openingand can withstand the high temperatures created by absorption Of thesolar energy. Again, an inside surface of the insulation closing theends of the triangular prism shaped opening may be a high emissivitysurface facing into the opening.

Outer surfaces of the receiver panels of the solar energy receiver arepreferably covered with insulation, which may comprise prefabricatedinsulation panels, to prevent heat loss from the outer surfaces byradiation or conduction.

The rectangular or “V” shaped openings in the bottom of panel assembliesmay be partially closed by insulating tiles or fused quartz panels (notillustrated) to restrict heat loss by convection while leaving smallerapertures through which solar energy may be directed from theheliostats.

The solar energy receiver may be mounted suspended from a tower andenergy is directed at the openings in the receiver by heliostats locatedaround a base of the tower. The solar energy receiver may be mounted ona side of the tower facing away from the equator and the heliostats maybe located predominantly on the opposite side of the tower to theequator although an East-West orientation is also possible.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of examplewith reference to the accompanying drawings in which:

FIG. 1 shows a Concentrating Solar Power (CSP) installation, including athermal storage receiver mounted on a tower in a heliostat field;

FIG. 2 shows a housing of a solar receiver panel used in the receiver ofFIG. 1 shown in plan, elevation, end elevation and perspective views;

FIG. 3 shows a perspective view of a heat exchanger coil used in thepanel of FIG. 2;

FIG. 4 a shows a partial perspective view of the heat exchanger coil ofFIG. 3 sitting on a base capping graphite plank;

FIG. 4 b shows a partial perspective view of the heat exchanger coil ofFIG. 3 showing insertion of a graphite plank adjacent to the basecapping plank seen in FIG. 4 a (viewed from a non-insertion end);

FIG. 4 c shows a partial perspective view of the heat exchanger coil ofFIG. 3 showing insertion of a graphite plank adjacent to the basecapping plank as seen in FIG. 4 b when viewed from the opposite end(i.e. the insertion end);

FIG. 4 d shows a cross-section of one of the planks seen in FIGS. 4 a, b& c illustrating a semicircular groove;

FIG. 4 e shows a cross-section of one of the planks seen in FIGS. 4 a, b& c illustrating a half obround groove;

FIG. 5 a shows a partial perspective view of the heat exchanger coil ofFIGS. 3, 4 a & 4 b, & 4 c with a number of a graphite planks insertedviewed from a second (non-insertion) end;

FIG. 5 b shows a perspective view of the heat exchanger coil of FIGS. 3,4 a & 4 b, & 4 c fully embedded in graphite planks, with a top cappingplank removed, viewed from a second (non-insertion) end;

FIG. 5 c shows a perspective view of an alternative coil and graphitearrangement comprising two of the heat exchanger coils of FIGS. 3, 4 a &4 b, & 4 c fully embedded in graphite planks in parallel, with a topcapping plank removed, viewed from a second (non-insertion) end;

FIGS. 6, 7, 8 & 9 show in perspective, plan, end elevation andelevation, an assembly of receiver panels forming a solar receiverhaving a rectangular prism opening;

FIGS. 10 to 15 show in perspective, plan and elevation, two furtherassemblies of receiver panels forming solar receivers scaled up from theFIG. 6 assembly;

FIGS. 16 to 23 show in perspective and end elevation views, six furtherassemblies of receiver panels forming solar receivers having atriangular prism opening (with open ends typically closed by insulationor optically transparent panels—not shown);

FIGS. 24 to 31 show in perspective and end elevation views, six furtherassemblies of receiver panels forming solar receivers having triangularprism openings, similar to those of FIGS. 16 to 23 with the ends of theopenings closed by further receiver panels;

FIGS. 24 to 47 show in perspective and end elevations views, eighteenfurther assemblies of receiver panels forming solar receivers havingtriangular prism openings, similar to those of FIGS. 16 to 23 with theopenings rotated towards the energy source (with open ends typicallyclosed by insulation or optically transparent panels—not shown);

FIG. 48 is a sectional side view of an assembly of receiver panelsforming solar receiver having two rectangular prism openings in astepped or vertically offset arrangement, showing insulation around thereceiver panels and panels closing the openings;

FIG. 49 is a sectional plan view of the receiver assembly of FIG. 48;

FIGS. 50 and 51 are perspective views from above and below of theassembly of FIGS. 48 and 49;

FIGS. 52 & 53 are perspective views from above and below of the assemblyof FIGS. 48 and 49 before the insulation is added;

FIGS. 54 & 55 are perspective views from above and below of an assemblysimilar to that of FIGS. 48 and 49 with narrower openings, before theinsulation is added;

FIGS. 56 & 57 are perspective views from above and below of an assemblysimilar to that of FIGS. 48 and 49 with openings of double the width,before the insulation is added;

FIG. 58 is a sectional side view of yet another assembly of receiverpanels forming solar receiver having two triangular prism openings in astepped or vertically offset arrangement similar configuration to thearrangement of FIG. 46, showing insulation around the receiver panels;

FIG. 59 is a sectional plan view of the receiver assembly of FIG. 58;

FIGS. 60 and 61 are perspective views from above and below of theassembly of FIGS. 58 and 59;

FIG. 62 is a sectional side view of yet another assembly of receiverpanels forming solar receiver having two triangular prism openings in astepped or vertically offset arrangement similar configuration to thearrangement of FIG. 38, optically clear panels closing the ends of theopenings;

FIG. 63 is a perspective view of the assembly of FIG. 62;

FIGS. 64 & 65 show perspective views from above and below of stillanother assembly of receiver panels forming solar receiver having twotriangular prism openings in side by side arrangement;

FIG. 66 is a sectional front elevation of the receiver assembly of FIGS.64 & 65;

FIG. 67 shows a perspective view of an alternative heat exchanger coilused in the panel of FIG. 2;

FIG. 68 shows a partial perspective view of the heat exchanger coil ofFIG. 67 sitting on a base capping graphite plank and showing insertionof a graphite plank adjacent to the base capping plank (viewed from anon-insertion end);

FIG. 69 shows a partial perspective view of the heat exchanger coil ofFIGS. 67 & 68 with a number of a graphite planks inserted viewed from asecond (non-insertion) end;

FIG. 70 shows a perspective view of the heat exchanger coil of FIGS. 67,68 & 69 fully embedded in graphite planks, with a top capping plankremoved, viewed from a second (non-insertion) end;

FIG. 71 shows a housing of a solar receiver panel similar to the housingof FIG. 2, but incorporating the heat exchanger arrangement of FIGS. 67to 70, shown in plan, elevation, end elevation and perspective views;

FIG. 72 shows a cross-section of two of the planks seen in FIGS. 68, 69,70 and 71 illustrating a half obround groove;

FIG. 73 is a perspective view from above of another assembly of receiverpanels forming solar receiver having two rectangular prism openings inside by side arrangement; and

FIG. 74 is a sectional view of an absorber panel showing a powder, suchas graphite powder which fills voids between the graphite core and thehousing and a reservoir containing additional powder to accommodatechanges in the volume of the void spaces in the absorber panel.

DETAILED DESCRIPTION

Referring to FIG. 1 of the drawings an example of a graphite solarenergy receiver 102 is shown mounted on a tower 101 within a field ofheliostats 106 whereby solar energy is reflected from the heliostatsonto receiving surfaces 107 of the solar energy receiver 102. The fieldof heliostats 106 and the solar energy receiver 102 are each preferablylocated generally on the side of the tower facing away from the equatoralthough an East-West orientation is also possible. The solar energyreceiver 102 is suspended from the tower by suspension elements 105 suchas cables or rods. A door 103 is hinged from one side of the solarenergy receiver 102 such that the solar energy receiver 102 can becovered to conserve energy during periods of low insolation (i.e. duringthe night or during periods excessive of cloud cover. The inner surface104 of the door 103 may be highly reflective (or highly emissive) toreflect energy falling on this surface onto the receiving surface 107when the cover is open. The solar energy receiver 102 is configuredusing a plurality of standard panels 111 of a type illustrated in FIGS.1 to 5 and described below. Note however that this receiver isillustrated by way of example and many different receiver configurationsare possible, some of which are described below.

In FIG. 2 an example of the outer housing of a receiver panel 111 isillustrated in plan, elevation, end elevation and perspective views. Thepanel housing comprises two large substantially flat parallel side walls12, 13 bounded by a bottom wall 14, end walls 15, 16 and a top wall 17to form a closed container. In use the panel 111 will typically beoriented vertically with the bottom wall 14 typically be located at alower end of the panel. In some cases however a panel 111 might be usedhorizontally with the side face 12 as the lower face. With reference toFIG. 2, in one form the housing has dimensions of 2214 (A)×1829 (B)×428(C) mm, however these dimensions may vary to optimize usage of graphitecut from standard dimension blanks and to optimize packing of completereceiver panels into a standard shipping container.

The bottom wall 14 of the housing may be integrally formed with the twoside walls 12, 13 by bending a single piece of wall material into a “U”shape in which the base transitions into each of the side walls via acurved bend of radius R which in the present example is in the range of50 to 180 mm and nominally 80 mm. The wall material is preferably asheet steel material capable of retaining structural integrity tosupport the enclosed graphite core, the heat exchanger and any heatexchange fluid contained therein at elevated temperatures of at least1000° C.

Mounting flanges 21 are provided extending from the end walls 15, 16 andinclude respective upper and lower mounting holes 23, 24. The flanges 21are used to suspend the panel from a mounting frame (not shown) bybolting them to the frame via the mounting holes 23, 24. Each flange maycomprise an extension of one of the end walls 15, 16 beyond therespective side wall 13 to which it is joined (i.e. the flange may becut from the same piece of sheet material as the end walls 15, 16 fromwhich they extend). By suspending the receiver panel from the flanges 21rather than supporting it from below, the resulting tension in the sidewalls due to gravity of the graphite core acting on the housing allowsthem to resist buckling to maintain good thermal communication with thegraphite core. The curved shape of the housing where the side walls 15,16 join the bottom wall 14 through a bend also tends to keep the metalwalls pressed against the graphite core. In addition, suspending thereceiver from above leaves the base of the receiver free of supportingstructure and associated protective insulation such that it may beexposed to and can absorb solar radiation from which it would otherwisebe protected, allowing more of the surface of the receiver panel 111 tobe used for energy absorption.

Vents 51 are provided in the top wall 17 of the housing to allow ventingduring welding together of the housing walls. These holes may be plugged(e.g. by welding after the panel walls are joined, or they may be usedto accommodate sealed cable ports through the wall to passinstrumentation cables such as thermocouple wires into the housing, asfill ports to provide an Argon blanket to the graphite core, toaccommodate a filling nozzle to fill the void space and/or an internalreservoir with graphite powder or other thermally conductive media, orto accommodate a connection to an external reservoir to maintain thelevel of such materials, when the graphite core and housing expand andcontract during thermal cycling.

Referring to FIG. 3, an example of a heat exchanger 20 is shown inperspective. The heat exchanger 20 is embedded in a graphite core asseen in FIGS. 4 a, 4 b, 4 c, 4 d, 4 e, 5 a, & 5 b (and in a differentconfiguration in FIG. 5 c). The heat exchanger 20 comprises heatexchanger tubing 25, 26, 27, 28, 39, 40 and first and second heatexchanger inlet/outlet 18, 19. The first and second heat exchangerinlet/outlets 18, 19 are interchangeable as inlet or outlet depending onthe direction in which it is desired to flow the heat exchange fluidthrough the heat exchanger in a particular application.

The heat exchanger tubes may be made, for example, from 253MA austeniticstainless steel (or any suitable high temperature thermally conductivematerial such as 800H austenitic steel or alloys such as Inconel), andmay have a nominal outside diameter of for example 42.16 mm in thepresent embodiment but the outside diameter may vary to be greater orsmaller than this depending on the particular circumstances of theapplication. For example, in other embodiments the heat exchanger tubesmay be made from the same or a similar material and may have a nominaloutside diameter of 26.67 mm. The heat exchanger tubing 25, 26, 27, 28,39, 40, the drain 29 and associated inlet/outlet tubes 18, 19 arepreferably formed with at least some of the tube assembly taking acoiled or serpentine form suitable for compression (like a spring)during assembly, such that when the housing 111 expands due to thermalexpansion, the resulting stresses from the movement of the pipeconfiguration does not exceed the mechanical properties of the pipematerial.

In an alternative arrangement, the drain 29 may also act as an inlet oroutlet in which case the inlet/outlet 18 will be redundant and might beremoved along with its connecting tubes 25 and 40 and passage of fluidthrough the heat exchanger will be (in either direction) between thedrain 29 and the inlet/outlet 19.

The heat exchanger tubing (as seen in FIG. 3) is preferably almost fullyembedded in the graphite core (see FIGS. 5 a, 5 b & 5 c), the first andsecond heat exchanger inlet/outlets 18, 19 extend through openings 55,56 in a top graphite capping plank 52, shown removed in FIG. 5 b and thewalls of the housing 111 as seen in FIG. 2. An end 38 of the heatexchanger drain 29 also extends through the housing (see FIGS. 2 and 4c) through a channel 54 in the graphite base plank 31. A riser 25connects the lower portion of the heat exchanger coil 26, 27, 28 to thefirst inlet/outlet tube 18 via a further tubing section 40, the riserpassing inside the connecting portions 27. The riser 25 and furthertubing section 40 are unconstrained by the graphite between the lowerend of the riser 25 where it joins to one of the straight tube portions26 of the lowest row, and the end of tubing section 40 where it joins tothe inlet/outlet tube 18. Thus these tubing sections are able to move toaccommodate expansion of the heat exchanger tubing in use, withoutexceeding the material limits of the tubing. A pair of longer coils 39connect the second inlet/outlet tube 19 to one of the straight tubeportions 26 of the highest row. These longer tubing coils are alsounconstrained by the capping plank 52 of graphite (See FIG. 5 b) whichis placed over them and are able to move to accommodate expansion of theheat exchanger tubing in use, without exceeding the material limits ofthe tubing. The top pair of longer coils 39 may be compressed (i.e.sprung together) prior to it being fixed to the top plate 17 (FIG. 2)during assembly of the heat exchanger and graphite into the housing toallow for thermal effects when the panel is in use. When the panel isheated from ambient to its working temperature, the outer walls of thepanel (particularly the side walls 12, 13) may reach up to 1000° C.,while the interior temperature of the graphite and the heat exchangertubing may reach 800° C. In these conditions the walls will expands byabout 19 mm per meter of length or about 40 mm in the preferredarrangement, however the graphite will only expand by about 3 mm permeter, resulting in a vertical growth of about 6 mm in the preferredarrangement. Thus the top of the graphite core will drop by about 34 mm.Therefore by compressing the longer coils 39 when the panel is assembledthese coils can spring apart as the top of graphite drops in the housingto accommodate the increases difference in distance between the top coilof the coils held captive in the graphite and the second inlet/outlettube 19 which is welded into the top of the housing. The problem is lesspronounced for the first inlet/outlet tube 18 as the riser 25 willexpand at a similar rate to the housing, however the horizontal tube 40will spring to accommodate any differences that do occur.

Referring to FIG. 5 c, an alternative arrangement is illustrated inwhich two sets of essentially identical heat exchanger tubing (as seenin FIG. 3 but with the riser 25 positioned slightly differently) ispreferably almost fully embedded in the graphite core in parallel, thefirst and second heat exchanger inlet/outlets 18, 19 extend throughwalls of the housing 111 similarly to the arrangement seen in FIG. 2 butwith a wider housing and two pairs of inlet/outlet tubes 18, 19corresponding to the two heat exchangers. Risers 25 connect the lowerportions of each of the heat exchanger coils 26, 27, 28 to therespective first inlet/outlet tube 18 via the further tubing sections40. The risers 25 and further tubing sections 40 are unconstrained bythe graphite between the lower end of the risers 25 where they join toone of the straight tube portions 26 of the lowest row of each heatexchanger, and the end of tubing sections 40 where they join to theinlet/outlet tubes 18. Thus these tubing sections of each heat exchangerare able to move to accommodate expansion of the heat exchanger tubingin use, without exceeding the material limits of the tubing. In eachheat exchanger, a pair of longer coils 39 connect the secondinlet/outlet tube 19 to one of the straight tube portions 26 of thehighest row. These longer tubing coils are also unconstrained by thecapping plank 152 of graphite (see FIG. 5 c) which is placed over themand are able to move to accommodate expansion of the heat exchangertubing in use, without exceeding the material limits of the tubing.

The housing is sealed around the first and second heat exchangerinlet/outlets 18, 19, and the end 38 of the drain 29 where they exit thehousing such that air cannot enter the housing after it is sealed. Theplurality of openings 51 in the top wall 17 of the housing (as seen inFIG. 2) act as vents during welding together of the wall panels. Thesevents may be sealed by welding after the rest of the panel has beenwelded together or they may be used as sealed cable ports for sensorssuch as thermocouples used to monitor conditions inside the panel inoperation, as fill ports to provide an Argon blanket for the graphitecore or to accommodate a filling nozzle to fill the void space with agraphite powder or other thermally conductive media. By excluding airfrom entering the housing, once it is heated to operating temperature afirst time, any oxygen in the housing will oxidize a small quantity ofgraphite forming carbon dioxide and after that no further reaction willoccur within the housing between the graphite and the residual aircontained in the housing. However as discussed above if the operatingtemperature of the panel is likely to exceed 700° C. in a particularinstallation, it will be desirable at manufacture to replace the airfilling the spaces in the panel between the graphite and the walls withan inert gas such as argon or helium.

The points where the first and second heat exchanger inlet/outlet 18, 19pass through the housing 111 are preferably in close proximity andpreferably exit through the top wall 17 of the housing, to assist withmounting and manifolding the pipes with other receivers.

The heat exchanger coils comprise a plurality of straight tube portions26 arranged in parallel and connected at their ends by connectingportions 27, 28 to form a serpentine coil. Preferably the straight tubeportions 26 are arranged in parallel planes forming rows of pairs ofstraight tube portions. The straight tube portions 26 in each row arealigned with the straight tube portions in adjacent rows such that theyalso exist in vertical planes perpendicular to the first mentionedparallel planes.

In the example illustrated in FIG. 3, the two straight tube portions 26in each row are connected together at their first end (the graphiteinsertion end) by first connecting tube portions 28 and at their secondend (non-insertion end) each of the two straight tube portions of eachrow are connected to straight tube portions 26 of each of two adjacentrows by second connecting tube portions 27. A first heat exchangerinlet/outlet tube 18 is connected to one of the straight tube portions26 in the bottom row via the riser tube portion 25 and the further tubeportion 40. A second heat exchanger inlet/outlet tube is connected toone of the straight tube portions 26 in a top row (the upper row in FIG.3) via the longer tube coils 39. As seen in FIGS. 4 a, 4 b & 5 a, theconnecting portions 27 are joined in the middle of their curve by a weld37 allowing the coils to be formed as individual rows comprising twostraight tube portions 26 joined at the first (graphite insertion) endby the first connecting portion 28 and having two halves of secondconnecting portions 27 angled respectively upwardly and downwardly forconnection (by welds 37) to the corresponding mating halves of thesecond connecting portions 27 of the rows above and below. Thus asupplier can manufacture the individual coil sections in bulk, as singlepieces bent from one piece of tube, each comprising two straight tubeportions 26 joined by a first connecting tube portion 28 and terminatedby two half connecting tube portions 27, and these can be easilytransported to the assembly factory for assembly into the finished coiland subsequent assembly into the receiver panel 111.

After the heat exchanger is fabricated, pre-shaped planks of graphite31, 32 & 52 are positioned to encompass most of the heat exchangertubes. Referring to FIG. 4 a, first a lower capping plank 31 ispositioned beneath the lowest row of straight tube portions 26. A secondcapping plank 52 (shown removed in FIG. 5 b to expose its lower surface)is positioned over the upper row of straight tube portions 26 after theremaining graphite planks 32 are in position. The lower capping plank 31is grooved on one (upper) surface groove having a semicircularcross-section conforming to the shape and radius of the straight tubeportions 26 and first connecting tube portion 28 at the first end of theheat exchanger. The edges 33 of the lower capping plank 31, between theface opposite the grooved surface (i.e. the downward facing surface inFIG. 4 a) and the sides of the capping plank 31, are radiused tocorrespond with the curved transition between the side walls 12, 13 andthe base wall 14 of the housing. The upper capping plank 52 has squarededges between the opposite face (i.e. the outward facing surface) andthe sides of the capping plank and the surface that abuts the topmost ofthe intermediate graphite planks 32 is recessed 53 to accommodate thetube section 40, the longer tube coils 39 and the inlet/outlet tubes 18,19 allowing them room to move with expansion and contraction as the heatexchanger, the graphite and the housing heat and cool. The inlet/outlettubes 18, 19 pass through the capping plank 52 (not visible) to accessthe openings in the housing top wall 17. To accommodate two longer coils39, the top capping plank 52 is thicker than the remaining graphiteplanks.

Referring to FIGS. 4 b, 4 c, 5 a & 5 b, the bulk of the graphite planks32 are positioned between the rows of straight tube portions 26 and therespective first connecting tube portions 28. The graphite planks 32each include two opposite surfaces in which the semicircular grooves 35,36 are formed (only upper grooves are visible in FIGS. 4 a, 4 b & 4 c),conforming to the shape and radius of the straight tube portions 26 andthe first connecting tube portions 28 at the first (insertion) end ofthe heat exchanger. Referring to FIG. 4 d, a partial cross section oftwo abutting planks 32 shows two pairs of aligned semicircular grooves35 encompassing a pair of pipes 26. When assembled between rows ofstraight tube portions 26 adjacent pairs of the planks 32 encompass andclosely conform to the respective straight tube portions 26 and firstconnecting tube portions 28. Referring to FIGS. 4 a, 4 b & 4 c thesecond ends of the graphite planks 32 are provided with a recess 34 toaccommodate the second connecting tube portions 27 joining straight tubeportions 26 from adjacent rows of straight tube portions. The weld joins37 in the centre of each connecting portion 27 are also located in therecesses 34 to allow inspection of the weld joins after assembly. Therecesses 34 also accommodate the riser 25 which connects the lower coilto the first inlet/outlet tube 18 and allows the graphite to almostcompletely fill the housing while allowing space for the riser 25 andthe second connecting portions 27 which each must pass through the endof the graphite planks 32. Because the graphite planks extend to theends of the housing and almost fully occupy the space within thehousing; the load of the graphite is spread evenly across the bottomwall 14 of the housing, allowing thinner material to be used. Also bymaximizing the area of graphite in contact with the walls andconsequentially minimizing void space, the heat transfer into thegraphite by insolation is maximized. Minimizing void space alsominimizes the amount of trapped air that is available to react with thegraphite when the panel is heated to it operating temperature. In thepresent embodiment the volume of void spaces within the housing notoccupied by graphite or tubing is generally in the range of 4-10% andtypically 5-7% of the internal volume of the housing (at the workingtemperature). Correspondingly the side panel of the housing, which isthe irradiated surface of the panel when in use, is generally backed bythe graphite core over all but 1-5% of its area and typically 2-3% (atthe working temperature) in the preferred embodiment.

Referring to FIG. 67, another example of a heat exchanger 670 is shownin perspective. This embodiment is primarily intended forsuperheater-only operation and comprises three parallel serpentineshaped tube assemblies each having an independent input and output. Theheat exchanger 670 is again embedded in a graphite core as seen in FIGS.68, 69 & 70. The heat exchanger 670 comprises heat exchanger tubing 678,682, 683, 684, 685, 686, 687 & 688, heat exchanger inlets 674, 675, 676and heat exchanger outlets 671, 672, 673. The lower tube section 686,687, 688 provide the three inlets 674, 675, 676 and connect to the lowerend of the main tube assembly comprising tube sections 678. The heatexchanger inlets 674, 675, 676 also act as drains. The upper tubesection 683, 684, 685 provide the three outlets 671, 672, 673 andconnect via tube sections 682 to the upper end of the main tube assemblycomprising tube sections 678. The tube sections 678, 682, 683, 684, 685,686, 687 & 688 are joined together by welds 681. The flow may bereversed in various applications such that the inlets may be 671, 672and 673 and the outlets may be 674, 675 and 676.

The heat exchanger tubes may again be made, for example, from 253MAaustenitic stainless steel (or any suitable high temperature thermallyconductive material such as 800H austenitic steel or alloys such asInconel), and may have a nominal outside diameter of for example 42.16mm in this embodiment but the outside diameter may vary to be greater orsmaller than this depending on the particular circumstances of theapplication.

The heat exchanger tubing 678, 682, 683, 684, 685, 686, 687 & 688 areformed with at least some of the tube assembly taking a coiled orserpentine form suitable for compression (like a spring) duringassembly, such that when the housing 111 expands due to thermalexpansion, the resulting stresses from the movement of the pipeconfiguration does not exceed the mechanical properties of the pipematerial.

The heat exchanger tubing (as seen in FIG. 67) is preferably almostfully embedded in the graphite core (see FIGS. 68, 69 & 70), the heatexchanger inlet tubes 686, 687, 688 extend through openings 697 in abottom graphite capping plank 698 and heat exchanger outlet tubes 683,684, 685 extend through openings 703, 704, 705 in a top graphite cappingplank 701, shown removed in FIG. 70. Referring to FIG. 71, the heatexchanger outlet tubes 683, 684, 685 extend through openings 711, 712,713 in the top of the housing 111 and the heat exchanger inlet tubes686, 687, 688 extend through openings 714, 715, 716 in the bottom of thehousing 111. As with the previous embodiments, these tubing sections areable to move to accommodate expansion of the heat exchanger tubing inuse, without exceeding the material limits of the tubing.

The housing is sealed around the heat exchanger inlet tubes 686, 687,688 where they exit the housing such that air cannot enter the housingafter it is sealed. The plurality of openings 51 in the top wall 17 ofthe housing (as seen in FIG. 71) act as vents during welding together ofthe wall panels. These vents may be sealed by welding after the rest ofthe panel has been welded together or they may be uses as sealed cableports for sensors such as thermocouples used to monitor conditionsinside the panel in operation, as fill ports to provide Argon blanket tographite core or as filling nozzle to fill void space with graphitepowder or other thermally conductive media.

After the heat exchanger is fabricated, pre-shaped planks of graphite689, 692, 701 are positioned to encompass most of the heat exchangertubes. Referring to FIG. 68, first a lower capping plank 689 ispositioned beneath the lowest row of inlet tube portions 686, 687, 688.A second capping plank 701 (shown removed in FIG. 70 to expose its lowersurface) is positioned over the upper row of outlet tube portions 683,684, 685 after the remaining graphite planks 692 are in position. Thelower capping plank 689 is grooved 691 on one (upper) surface groovehaving a semicircular (or preferably obround) cross-section conformingto the shape and radius of the outlet tube portions 683, 684, 685 of theheat exchanger. The edges 706 of the lower capping plank 689, betweenthe face opposite the grooved surface (i.e. the downward facing surfacein FIGS. 68, 69 & 70) and the top edges of the capping plank 689, areangled to correspond with the transition between the side walls 12, 13and the base wall 14 of the housing (see FIG. 71). The upper cappingplank 701 has squared edges between the opposite face (i.e. the outwardfacing surface) and the sides of the capping plank and the surface thatabuts the topmost of the intermediate graphite planks 692 is recessed696 to accommodate the tube section 683, 684, 685.

Referring to FIGS. 68, 69 & 70, the bulk of the graphite planks 692 arepositioned between the rows of tube portions 678. The graphite planks692 each include two opposite surfaces in which the semicircular (orpreferably semi-obround) grooves 691, 696 are formed, conforming to theshape and radius of the tube portions 678. When semi-obround grooves areused they are elongated in the vertical direction (i.e. two grooves abutto form an obround cross section with a vertical major axis) toaccommodate expansion of the tube assembly in the vertical direction (asviewed in FIG. 70). Referring to FIG. 72, a partial cross section of twoabutting planks 692 shows three pairs of aligned semi-obround grooves(691, 696) encompassing a pair of pipes 678.

Preferably the abutting surfaces of the graphite planks of FIGS. 4 a, 4b, & 4 c and FIGS. 68, 69 & 70 will have a surface finish which is N8 orbetter (ISO 1302). Such that when assembled between rows of straighttube portions adjacent pairs of the planks encompass and closely conformto the respective straight tube portions and first connecting tubeportions at the internal working temperature of the panel, which is upto 800° C., the grooves are made approximately 1.6% bigger than thenominal outside diameter of the tubes with a tolerance of approximately+0.00/−1.00%. For example, when the heat exchanger tubes are made from253MA austenitic stainless steel (any suitable high temperaturethermally conductive material such as 800H austenitic steel or alloyssuch as Inconel) and have a nominal outside diameter of 26.67 mm, thegrooves will preferably be 27.1 mm (+0.00/−0.25 mm) in diameter.Alternatively, when the heat exchanger tubes are made from the same orsimilar material and have a nominal outside diameter of 42.16 mm, thegrooves will preferably be 42.9 (+0.00/−0.25 mm) in diameter. To achievea high contact surface without excessive expense, the surface of thegraphite within the grooves will preferably have a surface finish whichis N7 or better (ISO 1302). By maximising the contact of the graphitewith the surface of the grooves by designing the grooves to be sizedappropriately for the tube diameter at the working temperature and byproviding appropriate surface finish, the operation of the heatexchanger within the graphite is enhanced.

Embodiments may also be manufactured in which the grooves 35, 36 (FIG. 4d) are elongated in cross section, rather than being semicircular. Inthis case the grooves may be a half obround shape with a radius which isslightly greater than the tube it encompasses (by about 1.6%) with astraight section about 1.6% of the radius in the direction perpendicularto (i.e. across) the parallel groove, to accommodate lateral movement ofthe tube when the coils expand. Referring to FIG. 4 e, a partial crosssection of two abutting planks 32 shows two pairs of aligned halfobround grooves 45 encompassing a pair of pipes 26. In the embodiment ofFIGS. 67 to 72, the grooves 691, 696 (FIGS. 68, 69, 70 & 72) are alsopreferably elongated in cross section, rather than being semicircular,however in this case the half obround shape is oriented with its majoraxis in the vertical direction in FIGS. 68, 69, 70 & 72. Referring toFIG. 72, the grooves 691, 696 may have a radius which is slightlygreater than the tube it encompasses (by about 1.6%) with a straightsection about 0.8% of the thickness of graphite plank, to accommodatevertical movement of the tube when the coils expand (refer to FIG. 69).However all of these arrangements have the disadvantage that the tubeswill not be as closely encompassed in the grooves and therefore thisarrangement might not always be appropriate and expansion of the coilsmay be accommodated by other means.

Because, in the embodiment of FIGS. 2, 3 4 a, 4 b, 4 c, 4 d, 4 e, 5 a, 5b and 5 c, the tube spacing between adjacent rows of tubes is less thana plank thickness in the finished receiver panel, the straight tubeportions need to be separated at the first (insertion) end while theplanks are inserted between the heat exchanger coils. This may beachieved by springing the first (insertion) ends of the straight, tubeportions 26 slightly apart to allow the planks to be easily insertedinto the fabricated heat exchanger tubing past the first connecting tubeportions 28 and by sliding them between adjacent rows of straight tubeportions 26 as illustrated in FIG. 4 b. Alternatively during fabricationof the heat exchanger coils, if they are spaced by a spacing greaterthan or equal to a plank thickness of the graphite planks 32 betweenwhich they are located in the final assembly (or if at least the first(insertion) ends are so spaced), the planks may be easily inserted intothe fabricated heat exchanger tubing between adjacent rows of coils andthe coils of the tubing may then be compressed into contact with thegraphite after insertion of the graphite planks 32 between the coils.Such springing is not required in the embodiment shown in FIGS. 67 to72.

The panel described with reference to FIGS. 67 to 72 and the panesdescribed with reference to FIGS. 2 to 5 may each be used in any of theassemblies described herein.

Once the graphite planks 31, 32, 52 are assembled to encompass the heatexchanger 20, (or planks 689, 692, 701 are assembled to encompass theheat exchanger 670) the assembly is inserted into the housing, locatingtubes are inserted into the holes 41 (or 702) extending through all ofthe planks to maintain alignment. At least one of the locating tubeswill engage a locating pin projecting from the base of the housing (notshown) to locate the graphite core 31, 32, 52 within the housing. Thehousing is then welded closed, including sealing the openings throughwhich the inlet/outlet tubes 18, 19 (or 686, 687, 688, 683, 684, 685)and the drain 29 (or 686, 687, 688) pass through the housing to form thefinished panel 111 (see FIGS. 2 & 71). The vent holes 51 are also sealedeither by welding or by inserting sealing plugs or a port fitting thatsealingly allows passage of transducer cables such as thermocouple wiresinto the interior of the panel. The vent holes 51 might also be fittedwith port fittings to be used as fill ports to provide Argon blanket tographite core or as filling nozzles to fill void space with graphitepowder or other thermally conductive media.

In the alternative arrangement shown in FIG. 5 c, two heat exchangersare used in parallel, each essentially the same as the heat exchanger ofFIG. 3. After the heat exchangers are fabricated, pre-shaped planks ofgraphite 131, 132 & 152 are positioned to encompass most of the heatexchanger tubes as in the single coil case. A lower capping plank 131 ispositioned beneath the lowest row of straight tube portions 26 and asecond capping plank 152 (shown removed in FIG. 5 c to expose its lowersurface) is positioned over the upper row of straight tube portions 26after the remaining graphite planks 132 are in position. The lowercapping plank 131 is grooved on one (upper) surface conforming to theshape and radius of the straight tube portions 26 and first connectingtube portion 28 at the first end of the heat exchanger. The edges 133 ofthe lower capping plank 131, between the face opposite the groovedsurface (i.e. the downward facing surface in FIG. 5 c) and the sides ofthe capping plank 131, are radiused to correspond with the curvedtransition between the side walls 12, 13 and the base wall 14 of thehousing. The upper capping plank 152 has squared edges between theopposite face (i.e. the outward facing surface) and the sides of thecapping plank and the surface that abuts the topmost of the intermediategraphite planks 132 is recessed 153 to accommodate the tube section 40,the longer tube coils 39 and the inlet/outlet tubes 18, 19 allowing themroom to move with expansion and contraction as the heat exchanger, thegraphite and the housing heat and cool. The inlet/outlet tubes 18, 19pass through the capping plank 52 (not visible) to access the openingsin the housing top wall 17. To accommodate two longer coils 39 of eachheat exchanger, the top capping plank 152 is thicker than the remaininggraphite planks.

Referring to FIG. 5 c, the bulk of the graphite planks 132 arepositioned between the rows of straight tube portions 26 and therespective first connecting tube portions 28. The graphite planks 132each include two opposite surfaces in which grooves are formed (notshown but similar to grooves 35, 36 in FIGS. 4 a, 4 b & 4 c), conformingto the shape and radius of the straight tube portions 26 and the firstconnecting tube portions 28 at the first (insertion) end of the heatexchanger. When assembled between rows of straight tube portions 26adjacent pairs of the planks 132 encompass and closely conform to therespective straight tube portions 26 and first connecting tube portions28. Referring to FIG. 5 c the second ends of the graphite planks 132 areprovided with a recess 134 to accommodate the second connecting tubeportions 27 joining straight tube portions 26 from adjacent rows ofstraight tube portions. The weld joins 37 in the centre of eachconnecting portion 27 are also located in the recesses 134 to allowinspection of the weld joins after assembly. The recesses 134 alsoaccommodate the risers 25 which connect the lower coils to each of thefirst inlet/outlet tubes 18 and allows the graphite to almost completelyfill the housing while allowing space for the risers 25 and the secondconnecting portions 27 which each must pass through the end of thegraphite planks 132. Again, because the graphite planks extend to theends of the housing and almost fully occupying the space within thehousing, the load of the graphite is spread evenly across the bottomwall 14 of the housing, allowing thinner material to be used. Assemblyin the double heat exchanger example illustrated in FIG. 5 c is similarto that of the single heat exchanger example described with reference toFIGS. 4 a, 4 b, 4 c, 5 a & 5 b.

Preferably a solar energy receiver will comprise two or more receiverpanels configured to form a downward opening cavity. The cavity may beformed with a combination of receiver panels and insulation panels.Outside surfaces of the receiver panels forming the solar energyreceiver will preferably be covered by insulation to minimize unwantedheat loss.

Referring to FIGS. 6, 7, 8 and 9 one possible configuration of a solarenergy receiver 102 (FIG. 1) is illustrated in perspective, plan, frontand side elevation respectively and comprises six heat absorbingreceiver panels 111 arranged in a rectangle around an opening 62. Theopening is capped by a panel 61 which may be either another heatabsorbing receiver panel similar to the other heat absorbing receiverpanels 111 or alternatively an insulating panel. The decision as towhether the panel 61 should be a heat absorbing or insulator panel willbe determined by whether energy from the heliostats 106 (FIG. 1) isincident on the panel. This will depend on the aspect ratio (height towidth) of the side panels 111 and the layout of the heliostats 106 inthe heliostat field. Usually energy will be reflected into the opening62 and onto bottom walls 14 of the vertical panels, but the outersurfaces would not usually be energy receiving surfaces.

FIGS. 10, 11 & 12 show perspective, plan and side elevations of a solarenergy receiver 102 similar to that of FIGS. 6, 7, 8 and 9 except thatit has two rectangular openings 62 formed by adding a further fourpanels 111 to the arrangement of FIGS. 6, 7, 8 and 9. Similarly FIGS.13, 14 and 15 show perspective, plan and side elevations of a solarenergy receiver 102 similar to that of FIGS. 10, 11 & 12 except that ithas three rectangular openings 62 formed by adding a further four panels111 to the arrangement of FIGS. 10, 11 & 12. In use the arrangements ofFIGS. 6 to 15 would include layers or panels of insulation (not shown inthese views) around the outside (and over the top when panel 61 is aheat absorbing panel) of each assembly to minimize heat loss though thenon absorbing outer surfaces (side wall 13 and top walls 17 and some endwalls 15, 16 in FIG. 2).

FIGS. 16, 17, 18 and 19 show perspective views and a side elevationrespectively of another three possible configurations of a solar energyreceiver 102. The side elevation of FIG. 19 is common to each of theembodiments shown in FIGS. 16, 17 & 18. The included angle of 36° isindicative only and can be up to 90° depending on the application,location and solar field design. The FIG. 16 embodiment comprises sixheat absorbing receiver panels 111 arranged in an inverted “V” shape tocreate an opening 162. Usually energy will be reflected into the opening162 and onto the bottom walls 14 of the vertical panels, but the outersurfaces would not usually be energy receiving surfaces. The FIG. 17embodiment has four panels and the FIG. 18 embodiment has two panelsforming receivers that are respectively ⅔ and ⅓ of the width of the FIG.16 embodiment.

FIGS. 20, 21, 22 & 23 show perspective views and a side elevationrespectively of another three possible configurations of a solar energyreceiver 102 similar to those of FIGS. 16, 17, 18 and 19 except thatthey are configured in two inverted “V” shapes with two openings 162 bydoubling the number of panels used in each case. As before in use thearrangements of FIGS. 16 to 23 would include layers or panels ofinsulation (not shown) over the outside surfaces of each panel 111 ofeach assembly to minimize heat loss though the non absorbing outersurfaces (side wall 13 and top walls 17 and some end walls 15, 16 inFIG. 2). The ends of the openings 162 could also be blocked byinsulating panels or optically transparent panels such as fused quartzpanels (not shown in these views).

The configurations of solar energy receivers 102 shown in FIGS. 24 to 31are similar to those of FIGS. 16 to 23 except that the openings 162 areclosed at their ends by additional heat absorber panels 241 similar tothe panels 111. FIGS. 32 to 47 show configurations similar to FIGS. 16to 31 except that in each case the solar energy receiver 102 is tiltedtoward the heliostat field 106 (in FIG. 1) such that panels 111 formingthe back surface of the opening 162 (i.e. furthest from the heliostatfield are vertical in use such that the inverted “V” shape and theopenings 162 are tilted to more directly face the heliostat field 106,but in FIGS. 40 to 47 the end panels 401 (similar to panels 111) are nottilted, such that an edge of the panel 401 aligns with an edge of therearmost panel 111 unlike end panels 241 in FIGS. 24 to 31.

A particularly advantageous configuration of a solar energy receiver 102is illustrated in sectional end elevation in FIG. 48 and in sectionalplan view in FIG. 49. FIGS. 50 and 51 are upper and lower perspectiveviews of the receiver of FIGS. 48 & 49. Perspective views withoutinsulation are seen in FIGS. 52 & 53, a version with a narrower openingis illustrated in FIGS. 54 & 55 (insulation no shown) and a two panelwide version is illustrated in FIGS. 56 & 57 (insulation no shown). Inthe FIGS. 48 & 49 configuration, a plurality of receiver panels 111 arepositioned in an offset fin configuration (as seen in FIG. 48 viewedfrom the side) in which the panels 111 form a plurality of spacedvertical fins 481 which are progressively offset upwardly from rearmostto foremost (with respect to the heliostat field) to form openings 486.Referring to FIG. 49, additional receiver panels 111 form end closures491 which close the ends of the openings 486. In FIGS. 48 and 49 thesolar energy receiver 102 is shown as having three fins but it will beappreciated that it could have two fins or it could have four or morefins. Similarly solar the energy receiver 102 is shown with only onepanel forming each fin 481, whereas the fins might be 2, 3 4 or morepanels long. The horizontal spacing “d” of the panels will be in theorder of 1 to 3 times the panel thickness (C in FIG. 2). The verticaloffset “a” of each panel relative to the one behind it will be in theorder of 0-2 times the panel thickness (dimension C in FIG. 2). Theoffsets “a” in FIGS. 39 & 47 will have similar values.

The walls of each housing are preferably fabricated from 253MAaustenitic stainless steel (or any suitable high temperature thermallyconductive material such as 800H austenitic steel or alloys such asInconel) finished to mill finish class 2B. The surfaces 191 of panels111 which face inwardly of the opening 486 and are forward facing withrespect to the heliostat field 106, have a natural class 2B mill finishto the stainless steel material to provide a degree of emissivity whichcauses a portion of the incident solar energy to be re-radiated onto thesurface 192 of the opposing panel 111, which is a rearward facingsurface with respect to the heliostat field 106. The rearward facingsurface 192 on the other hand will preferably be coated with a robusthigh temperature heat absorbing (black—specific absorptivity 0.80-1.0)paint, surface treatment or other suitable coating. Inwardly facingsurfaces of the side receiver panels 491 also have a natural class 2Bmill finish (specific emissivity 0.7) or polished surface (emissivity0.2) or may be provided with a further surface treatment or coating toachieve a medium emissivity surface (specific emissivity in the range of0.3-0.8) such that some of the solar energy falling on these panels isre-radiated to other internal surfaces within the opening 162.

The sides and top of the solar energy receiver 102 are surrounded withinsulating panels as with the earlier described arrangements. Inparticular the top of the openings 486 are closed with insulating panels485 which include high emissivity surfaces 487 facing into the opening486 to reflect any solar energy reaching the top of the openings 486back towards the heat absorbing surfaces of the fins 481. Insulatingpanels 483 are also located over the front (heliostat facing) surface ofthe front fin 481 and further insulating panels 483 are located over therear (non heliostat facing) surface of the rear fin 481. Insulatingpanels 492 also cover the outside surfaces of the side closure heatabsorbing panels 491.

Referring to FIGS. 58 to 61, another advantageous configuration of asolar energy receiver 102 is illustrated in sectional end elevation inFIG. 58 and in sectional plan view in FIG. 59. This panel configurationis similar to the FIGS. 46 & 47 embodiment, in which two triangularprism openings are formed in a stepped or vertically offset arrangement.In this example however the panels are shown with surroundinginsulation. FIGS. 60 and 61 are upper and lower perspective views of thereceiver of FIGS. 58 & 59.

In the FIGS. 58 & 59 configuration, a plurality of receiver panels 111are positioned in an offset inverted “V” configuration (as seen in FIG.58 viewed from the side) in which the panels 111 form a pair of spacedinverted “V” shaped openings 162 which are progressively offset upwardlyfrom rearmost to foremost (with respect to the heliostat field) to formthe openings 162. Referring to FIG. 59, additional receiver panels 111form end closures 401 which close the ends of the openings 162 toprevent convection losses from the opening 162 and to capture solarenergy directed from heliostats located towards the sides of theheliostat field 106, either by direct absorption or by reflection ontoanother surface within the opening 162. In FIGS. 58 and 59 the solarenergy receiver 102 is shown as having two inverted “V” shaped openingsbut it will be appreciated that it could have one inverted “V” shapedopening or it could have three or more inverted “V” shaped openings.Similarly solar the energy receiver 102 is shown with each inverted “V”shaped opening being only one panel long, whereas the openings might be2, 3 4 or more panels long. The vertical offset “a” of each pair ofpanels relative to the one pair behind it will be in the order of 0-2times the panel thickness (dimension C in FIG. 2) as was the case inearlier examples.

The walls of the housing are preferably fabricated from 253MA austeniticstainless steel (or any suitable high temperature thermally conductivematerial such as 800H austenitic steel or alloys such as Inconel)finished to mill finish class 2B. The surfaces 191 of panels 111 whichface inwardly of the opening 162 and are forward facing with respect tothe heliostat field 106, have a natural class 2B finish to the stainlesssteel material to provide a degree of emissivity which causes a portionof the incident solar energy to be re-radiated onto the surface 192,which is a rearward facing surface with respect to the heliostat field106. The rearward facing surface on the other hand will preferably becoated with a robust high temperature heat absorbing (black—specificabsorptivity 0.80-1.0) paint, surface treatment or other suitablecoating. Inward facing surfaces of the additional receiver panels 111which form end closures 401 have a natural class 2B mill finish(specific emissivity 0.7) to the stainless steel material, or may bepolished (specific emissivity 0.2) or polished surface (emissivity 0.2)or may be provided with a further surface treatment or coating toachieve a medium emissivity surface (in the range of 0.3-0.8) whichcauses a portion of the incident solar energy to be re-radiated ontoother internal surfaces of the opening 162.

As illustrated in FIGS. 60 & 61, the outward facing sides, fronts, backsand top of the inverted “V” assemblies of the solar energy receiver 102are surrounded with insulating panels as with the earlier describedarrangements. In, particular front (heliostat facing) outside surfacesof the panels 111 of each inverted “V” shaped assembly are covered byinsulating panels 583 & 585. Further insulating panels 582 & 584 arelocated over the rear (non heliostat facing) surfaces of each inverted“V” shaped assembly. Insulating panels 492 also cover the outsidesurfaces of the side closure heat absorbing panels 401. The tops of thereceiver panels 111 are each covered by additional insulation panels 586& 587 while edges of the panels 111 are covered by insulation panels591, 592 and 593. Additional insulation panels 589 cover those portionsof the inwardly facing surfaces of the side panels 401 extending abovethe sloping panels forming the front of the inverted “V” shape.

Referring to FIGS. 62 & 63, a further advantageous configuration of asolar energy receiver 102 is illustrated in end elevation in FIG. 62 andin perspective view in FIG. 63. In this panel configuration twotriangular prism openings 162 are formed in a stepped or verticallyoffset arrangement similar configuration to the arrangement of FIG. 38.In this example however the panels are shown with optically clear panels621 closing the ends of the openings (insulation panels not shown).

In the FIGS. 62 & 63 configuration, a plurality of receiver panels 111are positioned in an offset inverted “V” configuration (as seen in FIG.62 viewed from the side) in which the panels 111 form a pair of spacedinverted “V” shaped openings 162 which are progressively offset upwardlyfrom rearmost to foremost (with respect to the heliostat field) to formthe openings 162. Transparent panels 621, which may be fused quartz forexample, form end closures which close the ends of the openings 162 tolimit heat loss by convection while allowing solar energy to enter theopening 162 from the sides of the opening. In FIGS. 62 and 63 the solarenergy receiver 102 is shown as having two inverted “V” shaped openingsbut it will be appreciated that it could have one inverted “V” shapedopening or it could have three or more inverted “V” shaped openings.Similarly solar the energy receiver 102 is shown with each inverted “V”shaped opening being only one panel long, whereas the openings might be2, 3 4 or more panels long. The vertical offset “a” of each panelrelative to the one behind it will be in the order of 0-2 times thepanel thickness (dimension C in FIG. 2).

The walls of the housings in FIGS. 62 & 63 are preferably fabricatedfrom 253MA austenitic stainless steel (or any suitable high temperaturethermally conductive material such as 800H austenitic steel or alloyssuch as Inconel) finished to mill finish class 2B. The surfaces 191 ofpanels 111 which face inwardly of the opening 162 and are forward facingwith respect to the heliostat field 106, may have a natural class 2Bfinish to the stainless steel material (specific emissivity 0.7) or apolished surface (specific emissivity 0.2-0.3), or may be provided withanother suitable surface coating or treatment (specific emissivity inthe range of 0.3-0.8) which causes a portion of the incident solarenergy to be re-radiated onto the surface 192 on the inside of theopening, which is a rearward facing surface with respect to theheliostat field 106. The rearward facing surfaces 192 on the other handwill preferably be coated with a robust high temperature heat absorbing(e.g. black—specific absorptivity in the range of 0.8-1.0, preferably0.90-1.0) paint, surface treatment or other suitable coating.

A further embodiment is illustrated in FIGS. 64, 65 & 66 which shows aplurality of receiver panels 111 which are configured as a pair ofinverted “V” assemblies 641, 642, which are positioned side by side(i.e. in parallel) and suspended from a tower 101 (not shown in thisFigure). The configuration in this embodiment is similar to theconfiguration of FIG. 29, except that in this case the assembly ofreceiver panels is intended to be rotated so that the long axes of theopenings 162 are directed towards the heliostat field. The panels 111form a pair of inverted “V” shaped openings 162 and each inverted “V”assembly 641, 642 comprises four panels arranged as two side by sidepairs angled together to form a two panel long inverted “V” shapeassembly. In an alternative arrangement (not shown) each assembly 641,642 may have its plurality of inverted “V” shaped pair of panelsprogressively offset upwardly (by a distance “a”) from rearmost toforemost (with respect to the heliostat field—i.e. away from the tower)to provide better exposure of the solar energy to the entire assembly.As in the FIG. 29 embodiment one end (the rearward or tower end) of eachof the openings 162 is closed by another receiver panel 241. Howeverunlike the FIG. 29 embodiment, the other end of each opening 162 (theend facing the heliostat field) is partially closed by a transparentpanel 621, which may be fused quartz for example, form end closureswhich close the forward ends of the openings 162 to limit heat loss byconvection while allowing more solar energy to enter the opening 162from the centre of the heliostat field. In FIGS. 64, 65 and 66 the solarenergy receiver 102 is shown as having two side by side inverted “V”shaped openings 621 but it will be appreciated that it could have oneinverted “V” shaped opening or it could have three or more inverted “V”shaped openings. Similarly the solar energy receiver 102 is shown witheach inverted “V” shaped opening being two panels long, whereas theopenings might be 1, 3 4 or more panels long. The possible verticaloffset “a” of each pair of panels relative to the pair behind it(mentioned above but not illustrated) will be in the order of 0-2 timesthe panel thickness (dimension C in FIG. 2).

The openings 62, 162, 486 in the bottom of panel assemblies 102, 641,642may be fully or partially closed by insulating tiles or fused quartzpanels (not illustrated) to restrict heat loss by convection whileleaving smaller apertures through which solar energy may be directedfrom the heliostats.

The walls of the housings in FIGS. 64, 65 & 66 are again preferablyfabricated from 253MA austenitic stainless steel (or any suitable hightemperature thermally conductive material such as 800H austenitic steelor alloys such as Inconel) finished to mill finish class 2B. Thesurfaces 643 of panels 111 which face inwardly of the opening 162 andare forward facing with respect to the heliostat field 106, may have anatural finish to the stainless steel material (specific emissivity 0.7)or a polished surface (specific emissivity 0.2-0.3), or may be providedwith another suitable surface coating or treatment (specific emissivityin the range of 0.3-0.8) which causes a portion of the incident solarenergy to be re-radiated onto the surfaces 644, which are sidewaysfacing surfaces with respect to the heliostat field 106. The sidewaysfacing surfaces 644 on the other hand will preferably be coated with arobust high temperature heat absorbing (e.g. black—specific absorptivityin the range of 0.8-1.0, preferably 0.90-1.0) paint, surface treatmentor other suitable coating.

The outside surfaces of the sides fronts, backs and top of the inverted“V” shaped panel assemblies of the solar energy receiver 102 will besurrounded with insulating panels similar to those previously described,for example in the description of the FIG. 58-61 embodiment, with theexception that the transparent panels 621 will not be covered.

Referring to FIG. 73, another embodiment is illustrated which is avariation of the embodiments of FIGS. 6 to 15. In this case the absorberpanels 111 are similar to those of FIG. 71, with a plurality of parallelserpentine tube assemblies. The outlets 683, 684, 685 are locatedsimilarly to those of the FIG. 71 embodiment, however in this embodimentthe inlets 686, 687, 688 are located to enter through the lowerextremity of the rear end wall 16 (i.e. the wall furthest from theheliostat field), where they are protected from the solar energyreflected onto the assembly by the heliostat field. In this case, thepanels 111 are configured to create a plurality of openings 62 havingshapes which are rectangular prisms similar to those in FIGS. 6 to 15,however the mounting arrangement is different as the panels are hung byflanges 731, located at the top of the panels, via mounting holes 732.The flanges 731 may be extensions of the end walls 15 & 16. The tops ofthe openings 62 are closed by refractory panels 61 having lower (i.e.internal) surfaces which may be emissive (similar to emissive surfacesdescribed earlier). To minimise heat loss, surfaces of the receiverpanels 111 which are external surfaces of the receiver assembly may becovered by insulating panels (not shown for clarity but refer to earlierexamples). The rear of the assembly is closed by panels 734 which may berefractory panels (shown) with emissive surfaces (again similar toemissive surfaces described earlier) or may be absorber panels (such aspanels 111). The front of the assembly is closed by panels 733 which maybe transparent quartz panels or refractory panels with emissive surfacesfacing the interior of the cavity 62 (again similar to emissive surfacesdescribed earlier). The variations described in this embodiment may beincorporated in any of the previously described embodiments. In the topwall of the panels, openings 51 allow expansion of the internal airduring manufacture as with the previously described embodiments and maybe welded closed or used as ports. One of the openings 51 is shown witha filling nozzle 735 attached to permit filling of void spaces withgraphite powder (refer to description of FIG. 74 below).

FIG. 74 shows a receiver panel 111 with one side wall removed showingthe graphite planks 689, 692, 701 forming the graphite core. Voids willexist between the graphite planks and the walls of the housing (e.g.between the planks 689, 692, 701 visible in FIG. 74 and the wall whichhas been removed). A larger void 741 forms a reservoir between the topof graphite core and the top of the housing. The reservoir 741 and thevoids in this case are filled with graphite powder. The graphite powderenhances heat transfer between walls of the housing and the graphitecore. A filling nozzle 735 is in communication with the reservoir 741 toenable filling of the voids in the housing and topping up of thereservoir 731. The reservoir 731 stores additional graphite powder whichprevents spaces opening up when expansion and contraction of the housingand core occur during thermal cycling. This arrangement may be employedin any of the previously described embodiments.

By using modular receiver panels that can be assembled into a variety ofsolar energy receiver configurations, simple and fast site installationcan be achieved with minimal on site preparation requirements. Thereceiver panels can be shipped to site assembled and fully tested forsimple mounting on a tower along with associated insulation panels in apreferred one of a variety of optional configurations.

Reduced cost is achieved by simplification of design, having only 1basic panel design and a single basic configuration which is scalable byadding panels in a repeating pattern, thereby maximizing utilization ofkey materials and maximise graphite and heat exchanger piping costs as apercentage of the overall cost of installation.

In the preferred embodiment the receiver panel can be manufactured at asingle (off site) location from prefabricated parts supplied by perhaps2 to 4 suppliers. After assembly the panels may be sealed and QC testedat the manufactured site. Hence no further assembly or testing of thepanels is required on site. The panel design also optimizes usage ofgraphite and high pressure tubing which is manufactured in a very smallnumber of standard dimensions. Assembly of the panels into a solarenergy receiver on site is achieved by hanging the panels and thearrangement can be configured to suit different applications withvarying heat storage capacities by using multiples of the panel combinedto increase the size of the total assembly. Because the arrangement issuspended the lower surfaces 14 of the panels may be exposed to solarradiation and is no supporting base structure under the solar energyreceiver or heat shields to protect the base. Thus additional heat iscaptured by the hung panel through its base.

By using the planks of graphite stacked one on top of the other and hungwithin a clad ‘skin’ of the housing, the skin will be tensioned due togravity acting on the graphite core such that when the ‘skin’ expands attemperature, skin buckling which would otherwise reduce the transfer ofheat to the graphite is eliminated or at least minimized.

1. A solar energy receiver comprising a panel, the panel comprising agraphite core, a substantially gas tight housing encasing the graphitecore, a heat exchanger comprising heat exchanger tubing including a heatexchanger inlet and a heat exchanger outlet, the heat exchanger tubingat least partially embedded in the graphite core, the heat exchangerinlet and the heat exchanger outlet extending through the housing andthe housing sealed around the heat exchanger inlet and the heatexchanger outlet.
 2. The solar energy receiver of claim 1 wherein one ofthe heat exchanger inlet and the heat exchanger outlet comprises a heatexchanger drain.
 3. (canceled)
 4. The solar energy receiver of claim 1,wherein the housing has two spaced apart side walls joined togetherabout their periphery by one or more further walls to form a closedcontainer.
 5. The solar energy receiver of claim 4 wherein one of, or aportion of the one or more further walls is a bottom wall forming a baseof the housing and the graphite core is located in thermal communicationwith the base and at least one of the two side walls of the housing. 6.The solar energy receiver of claim 5 wherein at least two sides of thereceiver element are in thermal communication with the graphite core. 7.(canceled)
 8. The solar energy receiver as claimed in claim 5 whereinthe graphite core has a shape to conforming to an internal shape of thehousing and has a portion shaped to conform to an internal shape of thebottom wall of the housing.
 9. The solar energy receiver of claim 1,wherein the housing includes a plurality of. mounting flanges extendingfrom the housing and capable of suspending and supporting the weight ofthe receiver element, the mounting flanges extending including mountingholes therein. 10-11. (canceled)
 12. The solar energy receiver of claim9 wherein each mounting flange comprises an extension of one of the endwalls beyond the respective side wall to which it is joined.
 13. Thesolar energy receiver as claimed in claim 1 wherein the graphite corecomprises a plurality of stacked graphite planks, at least a lower oneof which is profiled to match the shape of the transition between thebase and the lower portions of the side walls of the housing.
 14. Thesolar energy receiver as claimed in claim 1 wherein at least some theheat exchanger tubes are in a coiled or serpentine form which iscompressed when the heat exchanger is at ambient temperature, such thatwhen the container expands due to thermal expansion under exposure tosolar energy, the compression of the compressed coiled or serpentinetubes is released. 15-16. (canceled)
 17. The solar energy receiver asclaimed in claim 14 wherein there are two or more coils in each panel.18. (canceled)
 19. The solar energy receiver as claimed in claim 2wherein the heat exchanger tubing and drain are arranged to allowdrainage of liquid from top of the heat exchanger to the bottom of theheat exchanger when the panel is angled from the vertical orientation byup to 21° to one side whereby none of the connecting tube portionspresent an uphill course for liquid draining from the top of the heatexchanger to the bottom. 20-25. (canceled)
 26. The solar energy receiveras claimed in claim 2 wherein the heat exchanger tubing is arranged toallow drainage of liquid from the top of the heat exchanger to thebottom of the heat exchanger and the heat exchanger inlet located at thebottom of a heat exchanger is also the drain outlet.
 27. The solarenergy receiver as claimed in claim 1 wherein shaped planks of graphiteare located between each row of tubes and capping planks are placed overthe inlet end rows of straight tube portions and the outlet end row ofstraight tube portions to encase a majority of the heat exchanger tubes.28. The solar energy receiver as claimed in claim 27 wherein thegraphite planks, other than the capping planks, each, include twoopposed surfaces, having grooves conforming to the shape and radius ofthe straight tube portions such that adjacent pairs of the planksencompass the respective straight tube portions. 29-37. (canceled) 38.The solar energy receiver as claimed in claim 1 wherein void spaceswithin the housing are filled with an inert gas.
 39. The solar energyreceiver as claimed in claim 1 wherein void spaces within the housingare filled with graphite powder.
 40. (canceled)
 41. The solar energyreceiver as claimed in claim 1 wherein the solar energy receivercomprises two or more receiver panels configured and mounted to form adownward opening cavity.
 42. The solar energy receiver as claimed inclaim 41 wherein the cavity is formed with a combination of receiverpanels and insulation panels.
 43. The solar energy receiver as claimedin claim 41 wherein the solar energy receiver comprises a plurality ofreceiver panels arranged to form an opening which is in a shape of arectangular prism. 44-114. (canceled)